The like valve assemblies are employed, e.g., in LIFD (Load-independent Flow Distribution) systems as known from WO 95/32364 A1 and Data Sheet RD 64 127/04.98 (Hydraulic Valves for Mobile Applications). An LIFD system includes, for instance, a variable displacement pump which may be regulated such as to generate at its output a pressure that is higher than the highest load pressure of all hydraulic consumers by a specific differential amount.
Each consumer is associated with a variable metering throttle with a downstream pressure compensator, with the latter maintaining the pressure drop across the metering throttle constant, so that the amount of pressure medium flowing to the corresponding hydraulic consumer depends not on the load pressure of the consumer or on the pump pressure, but solely on the open cross-section of the metering throttle. With the aid of the pressure compensators of the system it is achieved that in a case where the hydraulic pump was adjusted to the maximum stroke volume and the pressure medium flow is not sufficient for maintaining the specified pressure drop across the metering throttles, the pressure compensators of all of the actuated hydraulic consumers are adjusted in the closing direction, so that all the pressure medium flows are reduced by a same percentage. Due to this load-pressure independent flow distribution (LIFD), all of the actuated consumers move at a velocity that is reduced percentually by a same value.
In the solution in accordance with WO 95/32364 A1, if a consumer is supported for a prolonged period of time, it may happen that the latter will subside due to a small leakage flow between the work port subjected to pressure medium and the pressure medium tank of the system.
In order to avoid such a leakage flow, it is suggested in DE 196 46 447 A1 to insert in the respective work port a check valve that is capable of being controlled open and permits to shut off the work line leading to the consumer and subjected to pressure medium without any leakage. It is a drawback in this solution that considerable structural space is used up by mounting the check valve onto the work port.